One thing I should note about adding members to a group is that right now it will only accept users with a validated email address.  This doesn't mean that you can add an unvalidated user, it just means that the addition to the group is considered pending (you can actually see this in the menu) until they validate their email address.  Once they validate their email then they are automatically added to the group.  And when a user is pending it should send out a notice to the user that their group membership is pending on validation of their address.  I think this may be the reason why you're adding members, but not actually seeing them as members in your group.

We did this for security reasons, mostly, but having thought about this a little more (a user might not provide a valid email address at first, so how would they know their membership is pending?), we could change it around a little bit so that at least we could display to the user that their membership is pending while they're browsing the forum.  That, and it would help to show pending group membership options when you look at the group in the site manager.

Anyway, thank you for the feedback, this is really helping us fine tune things and get all the bugs worked out!